From: Crt Mori <cmo@melexis.com> To: Quentin Schulz <quentin.schulz@free-electrons.com> Cc: Jonathan Cameron <jic23@kernel.org>, jdelvare@suse.com, Guenter Roeck <linux@roeck-us.net>, Hartmut Knaack <knaack.h@gmx.de>, Lars-Peter Clausen <lars@metafoo.de>, Peter Meerwald-Stadler <pmeerw@pmeerw.net>, maxime.ripard@free-electrons.com, wens@csie.org, lee.jones@linaro.org, linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org, Linux Iio <linux-iio@vger.kernel.org>, linux-arm-kernel@lists.infradead.org, thomas.petazzoni@free-electrons.com, antoine.tenart@free-electrons.com Subject: Re: [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC Date: Wed, 20 Jul 2016 16:15:39 +0200 [thread overview] Message-ID: <CAKv63us_NoRq=B+koC823yCz_-7Dz8HerGLDbh3tkUW-zU4ecQ@mail.gmail.com> (raw) In-Reply-To: <f6e32bf0-f043-0d34-5190-18b89920bbfd@free-electrons.com> On 20 July 2016 at 14:37, Quentin Schulz <quentin.schulz@free-electrons.com> wrote: > On 18/07/2016 15:18, Jonathan Cameron wrote: > [...] >>> + >>> + if (!wait_for_completion_timeout(&info->completion, >>> + msecs_to_jiffies(100))) { >>> + ret = -ETIMEDOUT; >>> + goto out; >>> + } >>> + >>> + if (info->flags & SUNXI_GPADC_ARCH_SUN4I) >>> + *val = info->temp_data * 133 - 257000; >> Why report as processed? I'd just report them as raw with the scale >> and offset provided. It's not a big thing, but if we can leave it so >> that the conversion only occurs when desired, why not? >> >> For in kernel users, this all happen 'automagically' anyway ;) >> > > Mmmmh, in the code above we apply the scale on the raw value and then > the offset. While in iio_convert_raw_to_processed > (http://lxr.free-electrons.com/source/drivers/iio/inkern.c#L507), the > offset is applied before the scale. > > The way would be to factorize the computation by scale: > Now: *val = raw * scale + offset > Then: *val = (raw + offset/scale) * scale > > But the offset is an integer and offset/scale is therefore rounded. > Currently, we have the following values: > sun4i: -257000/133 = -1932.3308270676691 > sun5i: -144700/100 = -1447 > sun6i: -271000/167 = -1622.754491017964 > > Do we accept such rounding? How much does this rounding bring as mistake on end result and is this acceptable for you? You can always multiply it by 1000 or more to get the precision you want out. > > If not, we either stay with the processed value in read_raw or patch > inkern to add an offset to apply after having applied the scale to the > raw value (val2 from iio_channel_read is yet unused with > IIO_CHAN_INFO_OFFSET for example, we could use that to specify an > offset2 to apply after the switch(scale_type)-case). > > [...] > Quentin >
WARNING: multiple messages have this Message-ID (diff)
From: cmo@melexis.com (Crt Mori) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC Date: Wed, 20 Jul 2016 16:15:39 +0200 [thread overview] Message-ID: <CAKv63us_NoRq=B+koC823yCz_-7Dz8HerGLDbh3tkUW-zU4ecQ@mail.gmail.com> (raw) In-Reply-To: <f6e32bf0-f043-0d34-5190-18b89920bbfd@free-electrons.com> On 20 July 2016 at 14:37, Quentin Schulz <quentin.schulz@free-electrons.com> wrote: > On 18/07/2016 15:18, Jonathan Cameron wrote: > [...] >>> + >>> + if (!wait_for_completion_timeout(&info->completion, >>> + msecs_to_jiffies(100))) { >>> + ret = -ETIMEDOUT; >>> + goto out; >>> + } >>> + >>> + if (info->flags & SUNXI_GPADC_ARCH_SUN4I) >>> + *val = info->temp_data * 133 - 257000; >> Why report as processed? I'd just report them as raw with the scale >> and offset provided. It's not a big thing, but if we can leave it so >> that the conversion only occurs when desired, why not? >> >> For in kernel users, this all happen 'automagically' anyway ;) >> > > Mmmmh, in the code above we apply the scale on the raw value and then > the offset. While in iio_convert_raw_to_processed > (http://lxr.free-electrons.com/source/drivers/iio/inkern.c#L507), the > offset is applied before the scale. > > The way would be to factorize the computation by scale: > Now: *val = raw * scale + offset > Then: *val = (raw + offset/scale) * scale > > But the offset is an integer and offset/scale is therefore rounded. > Currently, we have the following values: > sun4i: -257000/133 = -1932.3308270676691 > sun5i: -144700/100 = -1447 > sun6i: -271000/167 = -1622.754491017964 > > Do we accept such rounding? How much does this rounding bring as mistake on end result and is this acceptable for you? You can always multiply it by 1000 or more to get the precision you want out. > > If not, we either stay with the processed value in read_raw or patch > inkern to add an offset to apply after having applied the scale to the > raw value (val2 from iio_channel_read is yet unused with > IIO_CHAN_INFO_OFFSET for example, we could use that to specify an > offset2 to apply after the switch(scale_type)-case). > > [...] > Quentin >
next prev parent reply other threads:[~2016-07-20 14:16 UTC|newest] Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-07-15 9:59 [PATCH v2 0/4] add support for Allwinner SoCs ADC Quentin Schulz 2016-07-15 9:59 ` Quentin Schulz 2016-07-15 9:59 ` [PATCH v2 1/4] hwmon: iio_hwmon: defer probe when no channel is found Quentin Schulz 2016-07-15 9:59 ` Quentin Schulz 2016-07-16 17:00 ` [v2,1/4] " Guenter Roeck 2016-07-16 17:00 ` Guenter Roeck 2016-07-18 10:02 ` Maxime Ripard 2016-07-18 10:02 ` Maxime Ripard 2016-07-18 13:29 ` Guenter Roeck 2016-07-18 13:29 ` Guenter Roeck 2016-07-15 9:59 ` [PATCH v2 2/4] iio: adc: add support for Allwinner SoCs ADC Quentin Schulz 2016-07-15 9:59 ` Quentin Schulz 2016-07-18 12:57 ` Maxime Ripard 2016-07-18 12:57 ` Maxime Ripard 2016-07-19 9:04 ` Quentin Schulz 2016-07-19 9:04 ` Quentin Schulz 2016-07-19 12:40 ` Maxime Ripard 2016-07-19 12:40 ` Maxime Ripard 2016-07-18 13:18 ` Jonathan Cameron 2016-07-18 13:18 ` Jonathan Cameron 2016-07-19 8:33 ` Quentin Schulz 2016-07-19 8:33 ` Quentin Schulz 2016-07-20 14:57 ` Jonathan Cameron 2016-07-20 14:57 ` Jonathan Cameron 2016-07-21 12:15 ` Quentin Schulz 2016-07-21 12:15 ` Quentin Schulz 2016-07-23 6:37 ` Jonathan Cameron 2016-07-23 6:37 ` Jonathan Cameron 2016-07-20 12:37 ` Quentin Schulz 2016-07-20 12:37 ` Quentin Schulz 2016-07-20 14:15 ` Crt Mori [this message] 2016-07-20 14:15 ` Crt Mori 2016-07-20 14:59 ` Jonathan Cameron 2016-07-20 14:59 ` Jonathan Cameron 2016-07-15 9:59 ` [PATCH v2 3/4] mfd: " Quentin Schulz 2016-07-15 9:59 ` Quentin Schulz 2016-07-18 13:02 ` Maxime Ripard 2016-07-18 13:02 ` Maxime Ripard 2016-07-19 12:04 ` Quentin Schulz 2016-07-19 12:04 ` Quentin Schulz 2016-07-18 13:25 ` Jonathan Cameron 2016-07-18 13:25 ` Jonathan Cameron 2016-07-19 7:31 ` Lee Jones 2016-07-19 7:31 ` Lee Jones 2016-07-20 15:01 ` Jonathan Cameron 2016-07-20 15:01 ` Jonathan Cameron 2016-07-21 12:12 ` Lee Jones 2016-07-21 12:12 ` Lee Jones 2016-07-21 20:08 ` Maxime Ripard 2016-07-21 20:08 ` Maxime Ripard 2016-07-22 13:55 ` Lee Jones 2016-07-22 13:55 ` Lee Jones 2016-07-23 6:42 ` Jonathan Cameron 2016-07-23 6:42 ` Jonathan Cameron 2016-07-25 9:55 ` Maxime Ripard 2016-07-25 9:55 ` Maxime Ripard 2016-07-19 8:35 ` Quentin Schulz 2016-07-19 8:35 ` Quentin Schulz 2016-07-15 9:59 ` [PATCH v2 4/4] hwmon: iio: add label for channels read by iio_hwmon Quentin Schulz 2016-07-15 9:59 ` Quentin Schulz 2016-07-15 14:03 ` Guenter Roeck 2016-07-15 14:03 ` Guenter Roeck 2016-07-15 14:36 ` Quentin Schulz 2016-07-15 14:36 ` Quentin Schulz 2016-07-16 2:53 ` Guenter Roeck 2016-07-16 2:53 ` Guenter Roeck 2016-07-18 12:24 ` Jonathan Cameron 2016-07-18 12:24 ` Jonathan Cameron 2016-07-19 6:55 ` Quentin Schulz 2016-07-19 6:55 ` Quentin Schulz 2016-07-20 14:49 ` Jonathan Cameron 2016-07-20 14:49 ` Jonathan Cameron
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